I’m a northerner who has always vented roofs. But I’m now going to roof a house with asphalt shingles in Brazil. I’ve read articles with different opinions regarding to vent or not. Joe L from the Building Science Corporation says not to vent. He argues that venting itroduces moist air and that venting doesn’t flush that much hot air. I read another article in JLC promoting venting in any climate. What do you all do?
One other question- Here they use clay or conrete tiles. There is a product they are promoting called Duralfoil that is a roll of some kind of aluminim foil that is supposed to reflect the radiation. Do you think this would cook the shingles too much? If I did use it would I put it down first or over the felt?
Edited 5/7/2006 7:15 am ET by McCarty12
Replies
The website for the foil is http://www.duralfoil.com.br The website is in Portugese but you can get a look at the material.
The argument against venting is at http://www.buildingscience.com/ Click on Joes Top Ten.
The argument for venting is in the Journal of Light Construction Jan 96 article " Vented or Unvented Roofs- The Great Debate."
First of all you need to look at the TOTAL picture that Joe is suggesting.
It is more than just venting the attic. It is conditioning the attic space so that the HVAC equpment and ducts are working in conditioned space.
Now a radiant barrier, which I assume that is what duralfoil is requires an 1/2 or more airspace againts the shiny side (if only one side is) and that can be either up or down.
And it does not "cook" the shingles.
The Florida Solar Institute has done tones of research on attic ventaltion, radiant barriers, insulation, roofing materials, and roofing colors.
Some of it has been published in JLC.
A google on Florida Solar Institute will help find their research.
So, are we saying that common concenus among those of experience is not yet all given over to the unvented roof concept?
I thought it was all cut and dried a year or two back.
be by the way....vent
half of good living is staying out of bad situations
Edited 5/7/2006 12:12 pm ET by rez
Thanks for the reply. I'll check out the Florida Solar Institute. I'm thinking now that the radient barrier might be difficult to apply if I need a 1/2 inch airspace. The roof is framed with Light gauge steel. The Duralfoil comes in 3ft rolls so I would have problems attaching it to the steel, furring owt the rafters with 1/2 inch material and then sheathing the roof without ruining the Duralfoil.
We won't be using a whole house system of air conditioning so there won't be any ductwork in the attic. We get pretty good breezes and it really isn't humid like Florida or even Wisconsin for that matter so I'll throw in some wall units when it's too hot to sleep. But the sun is killer. The only insulation I can come up with is fiberglass. So right now I'm thinking of not venting and putting fiberglass in the attic.
Feel free to express your comments,quips or criticisms.
From what I have heard the radiant barrier would be ideal for you climate.Don't know enough about the construction technic, but you can install it on the INSIDE of the sheathing/roof with the shinny side down into the open attic space.It does not have to be pointed "out" to work.In the southern states you can get sheathing with a foil surface on one side for a radiant barrier.